P0195 on Mercedes-Benz: Causes, Symptoms and Fix Cost

The Quick Answer above is the generic definition. What follows is the model-specific detail for the Mercedes-Benz models that log P0195.

Beyond the generic causes listed on the main P0195 page, these are the patterns noted for Mercedes-Benz models:

Follow these steps to pinpoint the root cause of P0195:

1. Read every stored code first and note whether P0195 arrived alone or alongside P0196, P0197 or P0198. Then read the freeze frame: a fault recorded on a cold start points at wiring, one recorded only when the engine was hot points at the sensor
2. Warm the engine fully and watch the live oil temperature value on a scan tool. A healthy engine settles somewhere around 90 to 110 C. A value pinned at the lowest or highest number the tool can display, or one that jumps around, is the fault you are chasing
3. Leave the car overnight, then compare oil temperature against coolant temperature and intake air temperature at key-on. On a cold engine all three should read within a few degrees of each other, so a large gap means the oil sensor is reporting nonsense
4. Find the sensor, which sits in the oil filter housing, the block or the underside of the sump depending on the engine, unplug it and look inside the connector for oil, water, green corrosion or spread pins. Clean and reseat it before condemning any parts
5. Test the circuit the way your sensor actually works, because most of the engines that set this code do not use a plain two-wire sensor. On a genuine two-wire thermistor, switch the ignition on and check for roughly 5 volts on one pin and a solid ground on the other, then unplug it and measure its resistance against the manufacturer figure for that temperature. On a BMW with the sump-mounted oil condition sensor there are three pins and nothing an ohmmeter can tell you: confirm the plug has battery voltage and a good ground, look at the single data wire with an oscilloscope, and check whether the alternator, the intelligent battery sensor, the glow module or the electric coolant pump have logged faults too, because they all share that BSD data line and one wiring fault can take several of them down together. On a VW Group G266 the three pins are battery voltage, ground and a pulse-width signal that runs to the instrument cluster, so check power and ground with a meter but read the actual value through the cluster with VCDS rather than probing for it. On Mercedes the sump sensor is pulse coded as well, so live data is the only meaningful test. Whichever type you have, wiggle the harness while watching the live value to catch an intermittent break
6. If sensor supply, ground and wiring all check out, fit an OEM or known-brand sensor, clear the code and drive one full warm-up cycle to confirm the reading tracks coolant temperature sensibly and the code stays away

Estimated repair costs for P0195 in EUR, compiled across makes. Expect Mercedes-Benz parts and labour towards the upper end of each range.

These codes are often seen alongside P0195 or point to related issues, on any make: